Will SquishPic be 64-bit compatible for macOS operating systems?
Yes -SquishPic is a 64-bit compliant application.
More information about 64-bit requirements and Apple's Operating System:
Apple has announced all new applications will be required to be 64-bit and macOS 10.14 Mojave will be the last Operating System to support 32-bit applications.
At WWDC, Apple announces macOS 10.14 (Mojave) will be the last macOS to support 32-bit applications.